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Commit2cd0acf

Browse files
author
Amit Kapila
committed
Prohibit shutting down resources if there is a possibility of back up.
Currently, we release the asynchronous resources as soon as it is evidentthat no more rows will be needed e.g. when a Limit is filled. This can beproblematic especially for custom and foreign scans where we can scanbackward. Fix that by disallowing the shutting down of resources in suchcases.Reported-by: Robert HaasAnalysed-by: Robert Haas and Amit KapilaAuthor: Amit KapilaReviewed-by: Robert HaasBackpatch-through: 9.6 where this code was introducedDiscussion:https://postgr.es/m/86137f17-1dfb-42f9-7421-82fd786b04a1@anayrat.info
1 parent07172d5 commit2cd0acf

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2 files changed

+20
-6
lines changed

2 files changed

+20
-6
lines changed

‎src/backend/executor/execMain.c

Lines changed: 12 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1726,8 +1726,12 @@ ExecutePlan(EState *estate,
17261726
*/
17271727
if (TupIsNull(slot))
17281728
{
1729-
/* Allow nodes to release or shut down resources. */
1730-
(void)ExecShutdownNode(planstate);
1729+
/*
1730+
* If we know we won't need to back up, we can release
1731+
* resources at this point.
1732+
*/
1733+
if (!(estate->es_top_eflags&EXEC_FLAG_BACKWARD))
1734+
(void)ExecShutdownNode(planstate);
17311735
break;
17321736
}
17331737

@@ -1773,8 +1777,12 @@ ExecutePlan(EState *estate,
17731777
current_tuple_count++;
17741778
if (numberTuples&&numberTuples==current_tuple_count)
17751779
{
1776-
/* Allow nodes to release or shut down resources. */
1777-
(void)ExecShutdownNode(planstate);
1780+
/*
1781+
* If we know we won't need to back up, we can release
1782+
* resources at this point.
1783+
*/
1784+
if (!(estate->es_top_eflags&EXEC_FLAG_BACKWARD))
1785+
(void)ExecShutdownNode(planstate);
17781786
break;
17791787
}
17801788
}

‎src/backend/executor/nodeLimit.c

Lines changed: 8 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -134,8 +134,14 @@ ExecLimit(PlanState *pstate)
134134
node->position-node->offset >=node->count)
135135
{
136136
node->lstate=LIMIT_WINDOWEND;
137-
/* Allow nodes to release or shut down resources. */
138-
(void)ExecShutdownNode(outerPlan);
137+
138+
/*
139+
* If we know we won't need to back up, we can release
140+
* resources at this point.
141+
*/
142+
if (!(node->ps.state->es_top_eflags&EXEC_FLAG_BACKWARD))
143+
(void)ExecShutdownNode(outerPlan);
144+
139145
returnNULL;
140146
}
141147

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